The present invention relates to a multi-band antenna, preferably a dual-band one. Said antenna is preferably formed on a printed circuit board (PCB).
In particular, the antenna according to the present invention is designed for communicating within two electromagnetic spectrum portions reserved for non-commercial radio-communication applications, normally referred to as ISM (Industrial, Scientific and Medical) or SRD (Short Range Device) bands. More in detail, the antenna according to the present invention is preferably adapted to operate in bands around the 868 MHz frequency, called European SRD band, the 915 MHz frequency, called ISM band, and the 2.4 GHz frequency, also called ISM band.
It is known that the free ISM and SRD frequencies are widely used for short-range data transmission in applications such as, for example, remote monitoring and control, such as wireless sensor and actuator networks (WSN/WSAN), telemetry, alarm systems, etc. These bands are used by several low-data rate and high-data rate communication standards, such as Wi-Fi, IEEE 802.15.4, Bluetooth, ZigBee, etc.
The devices adapted to communicate over said bands lead to applications developed through highly pervasive and device-dense systems; since said bands are widely used, they require that the cost of the device itself, and hence of the antenna which is a part thereof, is low.
In particular, in this field it is desirable to create a low-cost antenna that can be associated with consumer electronic devices.
Electronic devices, e.g. wireless ones, capable of operating over two or more ISM/SRD bands, are normally equipped with two or more antennae, which are substantially independent and distinct, and which are adapted to be selectively powered for the purpose of energizing the resonance modes of either antenna, depending on the frequency at which the device needs to communicate.
The duplication of the electronic devices and of their control logic leads to higher costs incurred for manufacturing and assembling the electronic device and to higher complexity of the device's control program, which is more subject to programming errors and bugs.
PCB antennae are also known which can operate at two different frequencies, in that they include two independent antennae arranged on the same layer of insulating material or at different levels of a printed circuit.
Even with such integration, however, the problem of selectively controlling the antenna that must be in operation at a certain moment has not been solved.
PCB antennae, or patch antennae, have a directional radiation diagram; in fact, they have the maximum radiation lobe in a direction substantially perpendicular to the surface of the printed circuit board on which the antenna is provided.
Patent applications are also known which describe non-linear antennae wound around themselves, in particular consisting of straight sections so structured as to create a spiral-wound broken line, thus minimizing space occupation.
Another known problem concerns the cross-talk between two near antennae, which, although they operate at different frequencies, interact electromagnetically with each other.
Such problems can be found in patent applications U.S. Pat. No. 7,692,600 and GB2347792.